This invention relates to a process for preparing agglomerates or granules of sodium perborate monohydrate (PBS-1) in which PBS-1 primary particles prepared by dehydration of sodium perborate tetrahydrate (PBS-4) are subjected to a compacting pressing-agglomeration process and subsequent comminution, as well as to the PBS-1 granules obtained by the process of the invention.
Sodium perborate monohydrate is a boron oxygen compound which (contrary to the trade name) is essentially free from water of crystallization, which contains peroxy groups and has the composition NaBO.sub.2 (OH).sub.2 or "NaBO.sub.3.H.sub. 2 O". A characteristic structural feature of this substance is the anion ring illustrated as follows: ##STR1## The active oxygen content of PBS-1 is generally 15 to 16 wt. %. The preparation of perborate monohydrate by dehydrating perborate tetrahydrate is known in the art. U.S. Pat. No. 3,914,380 and UK patent Application No. GB 1,520,127 describe the preparation of attrition-resistant sodium perborate monohydrate by dehydration of sodium perborate tetrahydrate obtained by crystallization in which a relative humidity level of 40 to 80%, and preferably of 50 to 70%, is maintained in the air surrounding the crystal grains and the temperature of the exhaust gas is maintained at a minimum of 60.degree. C. in order to achieve partial melting of the perborate.
Although it is possible according to the state of the art to prepare an attrition-resistant PBS-1 with excellent properties, particularly with respect to attrition resistance and rate of dissolution, such PBS-1 is insufficiently compatible with constituents of dishwashing agent formulations for use in dishwashers, and it would also be desirable if such sodium perborate monohydrate could be further improved with respect to its stability in powdered laundry detergent formulations.